The long-term goal of my research is to understand regulation of gene expression and genetic recombination in molecular terms. I have selected the temperate bacteriophage lambda as a particularly useful material for this purpose. My specific objectives are to achieve an understanding of the biochemical details of the following aspects of the lambda life cycle: (1) regulatory events which specify the lysogenic pathway of lambda development; (2) regulatory events which specify the lytic pathway; (3) the interaction of phage lambda with the host, in particular the mechanism by which the choice between lysis and lysogeny is achieved; (4) the site-specific recombination event which inserts the lambda DNA into the host DNA; (5) general recombination between phage DNA molecules during lytic growth. To try to achieve these objectives, we will use three levels of experimental analysis: (1) genetic experiments to identify the genes and define in very general terms how they work; (2) biochemical measurements of in vivo events, to suggest possible molecular mechanisms; (3) biochemical measurements in vitro with separated components, to establish molecular mechanisms.